The invention concerns a method in automatic arc welding of regulating the weld parameters of a weld joint between two workpieces, said method comprising deriving a characteristic value from electrical quantities of the arc at least on two separate occasions, which arc is made to oscillate across the groove between the workpieces, thereafter combining mathematically the values obtained on these occasions and comparing the result thus obtained with a rated value, i.e. the most favourable value, the departure of said obtained result from said rated value being used to affect means to set the weld parameters so as to ensure that the departure is maintained at a minimum value.
The purpose of the subject invention is to provide a method of controlling the weld parameters in the welding together of two workpieces to ensure that a homogeneous weld with an optimum root bead is obtained also when the distance separating the two workpieces or other factors affecting the weld vary.
To obtain an acceptable weld in automatic arc welding, it is necessary in welding root beads that the weld parameters are adjusted to the dimensions of the weld, particularly to the gap width. Automatic welding has hitherto been effected with fixed weld parameters, and consequently the demands on groove exactness have been high. These demands are often difficult to meet, both from a technical and an economical point of view.
It is consequently desirable to adjust the weld parameters to the groove, or in other words to control the weld parameters adaptively. The weld parameters usually are the electrode speed, the current intensity, alternatively wire feed speed, the tension and, in case of oscillation, the amplitude. Control may be effected by measuring the dimensions of the weld but that method requires separate transducers. However, in practice separate transducers are difficult to use. They are exposed to sprays, radiation and heat, all of which reduces their performance and serviceability. In welding grooves that are in not easily accessible positions, the groove cannot either be measured while the welding is in progress. By using the electrical arc proper as a transducer the disadvantages outlined above may be eliminated.
One example of the use of the arc as a transducer is shown by the groove sensing principle disclosed in DE OS No. 26 31 250. In accordance with the teachings of this publication the arc is oscillated in the groove and the electrical quantities at the extremes are compared. In automatic welding operations groove sensing alone is often not enough, however, but as mentioned above adaptive control of the weld parameters is also necessary. One example of such control while using the arc as the transducer is described in U.S. 3 233 076. However, this prior-art method requires that the welding head is maintained at an exact and constant distance from the groove, which requires separate transducers and therefore causes the disadvantages mentioned above.
The subject invention has for its purpose to provide a method in which the disadvantages outlined above are eliminated.